The present invention relates to integrated circuit amplifiers and, more particularly, to an integrated current amplifier circuit which combines bipolar and MOS circuit technology.
There are many applications which require combined accurate current amplification and a high impedance output. In addition, such applications can require a current amplification circuit that must operate over a wide voltage supply range, for example, 2-to-125 volts while maintaining accurate current amplification. One such application may be for use in today's automotive systems wherein it is desired to provide a low impedance series switch between the automobile's battery and downstream electronics.
Because of problems peculiar to the automotive industry, automotive manufacturers specify that the electronics must operate with a battery voltage of as low as four volts and as high as twenty-four volts while withstanding short voltage transients of .+-.125 volts. Under high voltage transients the battery must be disconnected from the electronics, which are typically integrated circuits, by an overvoltage protection scheme. This, overvoltage protection scheme must exhibit a low impedance path between the battery and the downstream electronics to enable operation thereof under the aforesaid low battery conditions. One method for providing overvoltage protection having the above described characteristics might be to design an integrated circuit having a high voltage, series-pass PNP transistor which would have its emitter-collector path coupled between the automobile's battery terminal and electronics. Control circuitry could then be coupled to the base of the PNP transistor to control its conduction. Hence, in response to high voltage transients, the control circuitry would turn-off the series-pass transistor to protect the downstream electronics. Under low voltage conditions, the PNP transistor provides a minimum voltage drop between the battery terminal and the downstream electronics to allow operation thereof
Among other requirements, the aforedescribed control circuitry must also provide accurate current gain to control the base current drive of the series-pass PNP transistor. Thus, a need exists for an accurate current gain amplifier.
In order to provide the above, the present invention contemplates combining bipolar PNP high voltage transistor, high voltage DMOS field effect transistor and low voltage NMOS field effect transistor technology.
Accordingly it is an object of the present invention to provide an improved current amplifier circuit.
Still another object of the present invention is to provide an improved integrated current amplifier circuit.
A further object of the present invention is to provide a current amplifier comprising a bipolar and MOS integrated circuit transistors.
A still further object of the present invention is to provide a BIMOS current amplifier integrated circuit having a constant amplification factor.
An additional object of the present invention is to provide a current amplifier having an active turn off scheme for ensuring that no current is produced at the output of the amplifier when the amplifier is suppose to be in an off state.